1. Field of the Invention
The present invention relates to negative resist composition and patterning process using the same.
2. Description of the Related Art
It is known that finer pattern rules are demanded with highly integrated LSI's providing highly increased speeds. This has correspondingly led to largely changed exposure methods and resist compositions, and particularly, KrF or ArF excimer laser light, electron beam, or the like are used as exposure light sources upon conduction of lithography of patterns at 0.2 μm or less, in a manner to adopt chemically amplified resists as a photoresist, which exhibit excellent sensitivities to such high energy radiations and provide higher resolutions.
Resist compositions are classified into a positive type where exposed areas are made to be dissolvable and a negative type where exposed areas are left as a pattern, and that one of them is selected and used, which can be more conveniently handled depending on a required resist pattern. Further, chemically amplified negative resist compositions are each typically configured to contain: a polymer dissolvable in an aqueous alkaline developer; an acid generator to be decomposed by exposure light to produce an acid; and a crosslinking agent for forming cross-linkages among polymer molecules with the aid of the acid as a catalyst, thereby making the polymer to become insoluble in the developer (the polymer compound and the crosslinking agent are integrated with each other, in some cases); as well as a basic compound for restricting diffusion of the acid produced by the typical exposure.
Negative resist compositions of a type configured to adopt phenol units as alkali-soluble units constituting a polymer compound to be dissolved in the aqueous alkaline developer, have been numerously developed, and particularly for exposure by a KrF excimer laser light. Since phenol units of these compositions do not exhibit light transmittivity in the case of exposure light having wavelengths in a range of 150 to 220 nm, the compositions have not been used for ArF excimer laser light. However, such negative resist compositions have been recently noticed again as ones for EB and EUV exposure which are exposure methods for obtaining finer patterns, and reports thereof are found in Japanese Patent Application Laid-open (kokai) Nos. 2006-201532, 2006-215180, 2008-249762, and the like.
Further, examples of characteristics to be demanded for resist compositions in the case of the resist elaboration as noted above, include not only a higher resolution which is a fundamental performance of a resist, but also a higher etching resistance. This is because, progressively finer patterns necessitate to progressively decrease thicknesses of resist films. Known as one technique for obtaining such a higher etching resistance, is a method, which also has been disclosed in Japanese Patent Application Laid-open (kokai) No. 2008-249762, to introduce, as subsidiary components of the polymer: a polycyclic compound such as indene, acenaphthylene or the like, which includes an aromatic ring(s) and a non-aromatic ring(s), and in which the non-aromatic ring has a carbon-carbon double bond conjugated with the aromatic ring; into a polymer having hydroxystyrene units.
In turn, as polymers for positive resists, it has been proposed to use a polymer having only indene structures such as described in Japanese Patent Application Laid-open (kokai) No. 2004-149756, while another method has been proposed in Japanese Patent Application Laid-open (kokai) No. 2006-169302 to use units having acenaphthylene structures by combining them with a hydroxystyrene derivative.
However, in trying to conduct such a fine processing that gaps between line widths are decreased down to as narrow as 50 nm which is demanded in the presently most-advanced processing technique, bridges are caused between pattern lines even by variously conducting a fine control by adopting a polymer system which has been conventionally presented for a negative resist composition, thereby making it difficult to form a fine pattern.